3 Expansion

Expansion in a command shell is somewhat like macro expansion in macro
parsers (such as cpp and m4), but in a command
shell, they are less often used for constants, and usually for using
variables and string manipulation.1 For example, $var on a line
expands to the value of the variable var when the line is
executed. Expansions are usually passed as arguments, but may also be
used as commands.2